Virtual line switched ring

ABSTRACT

At least one protection line is shared among SONET rings. Identification and availability information of the shared protection line is distributed among the switches of the SONET rings using K-byte data in the SONET overhead.

RELATED APPLICATIONS

[0001] This application is related to U.S. patent application Ser. No.09/259,263, filed Mar. 1, 1999, entitled “ROUTING AND SIGNALING IN ASONET NETWORK”, incorporated by reference herein.

BACKGROUND OF THE INVENTION

[0002] The present invention relates to a method and system forimplementing a virtual line-switched ring network; such as a lineswitched ring network carrying optical signals in accordance with asynchronous optical network (SONET) standard.

[0003] SONET networks often have a ring configuration including acollection of nodes forming a closed loop. FIG. 1 illustrates an exampleof a conventional SONET bidirectional ring 100 whereby information mayflow in either a clockwise or counterclockwise in the figure, asindicated by arrows labeled “working” and “protect”. Add-dropmultiplexers (A/D mux) 110, 120, 130 and 140 add and/or drop signals toswitch data from one span (SP1 to SP7) to another. Ring 100 is thustermed a “bidirectional line switched ring” or BLSR, and datatransmitted in such a ring typically must conform to a particularprotocol.

[0004] As further shown in FIG. 1, each of spans SP1 to SP7 includes oneworking line and a corresponding protection line. For example, spans SP1and SP5 interconnect A/D muxes 110 and 120 and include working linescarrying data in opposite directions. The working lines within each ofthese spans further include respective protection lines for transmittingdata in the event the associated working line fails.

[0005] The SONET ring provides protection for transmission of data intwo way. First if a working lines fails, the corresponding protectionlines may be used. In the alternative, if working lines fail between twoA/D muxes, any communication route directed through the failed line maybe rerouted through the A/D muxes through a process known as spanswitching. For example, if the working lines between A/D mux 110 and A/Dmux 120 fail, instead of using the corresponding protection lines,communications may be sent from A/D mux 110 to A/D mux 120 via A/D mux140 and 130.

[0006] Typically, the working and protect lines are provided in a fiberoptic bundle. Accordingly, if the working line fails, due to a fibercut, for example, the corresponding protect line often will also fail.Span switching is thus often preferred to simply switching data from thefaulty working line to the protect line. Both schemes may be used inconjunction with each other, however, whereby an attempt is first madeto use the protect line when the associated working line fails, andthen, if the protection line is itself faulty, span switching is used toredirect communications.

[0007] The SONET standard has a plurality of optical levels and logicallevels that represent the amount of optical information a line iscapable of carrying at a given time. These different optical levels arereferred to as OC-n, where n is indicative of the bandwidth or capacityassociated with the line. Current SONET bidirectional rings require thatall spans carry data at the same optical rate because A/D muxes can onlydirect communications from one line to another having the same OC-nlevel. Therefore, BLSR requires that all lines in the network are of thesame type and that each span between A/D muxes has the same number oflines.

[0008] In accordance with the SONET standard, spans transfer units ofinformation called Synchronous Transport Signals (STS). For thedifferent optical carrier levels OC-n (such as OC-1, OC-3 and OC-12),there is a corresponding STS-n, where n is the number of STS-1 segmentsor time slots. Typical spans are composed of 1, 3, 12, 48, or 192STS-1's. All SONET spans transmit 8,000 frames per second, where eachframe is composed of an integer number of STS-1 segments, such as 1, 3,12, 48 or 192.

[0009] Each STS-1 segment includes a payload section and an overheadsection. The overhead includes K-bytes that communicate error conditionsbetween spans in a network and allow for link recovery after networkfailure. K-byte signaling takes place over the protection lines. In aseries of STS segments, only K-bytes from the first STS-1 segment areused to carry error data. Current SONET networks make no use of theframing overhead of the remaining STS-1 segments. The series of STS-1segments only carries K-byte error information for a single ring.

[0010]FIG. 2 illustrates an example of a connection between two rings200 and 210 using four SONET A/D multiplexors. Specifically, A/D mux 202of ring 200 is coupled to A/D mux 212 of ring 210, while A/D mux 206 ofring 200 is coupled to A/D mux 216 of ring 210. Data is transmitted onthese connections at a slower rate than through rings 200 and 210. Thus,a total of four “matched” A/D mux nodes are often required to connecttwo rings. Typically, each such pair of A/D muxes is dedicated toproviding ring-to-ring connections, and are not configured to passinformation around a ring and forward information to another ring at thesame time.

[0011] In the SONET network ring environment, there currently does notexist a ring configuration that allows for spans within a single ring tohave different bandwidth or for a different number of lines to existbetween nodes. In addition, no current SONET network ring allows forsharing protection lines between different rings. Finally, current SONETnetwork rings do not allow for connecting rings using a single node.

SUMMARY OF THE INVENTION

[0012] Systems and methods consistent with this invention allow forsharing a ring using a single node by using switches at the nodes inplace of A/D multiplexors. Systems and methods consistent with thisinvention allow for sharing a protection line between different rings byutilizing unused overhead in frames sent between switches. Systems andmethods consistent with this invention allow for using a differentnumber and type of fibers or lines between switches in the same ringnetwork by using switches and an algorithm to control changing lines inthe ring.

[0013] Systems and methods consistent with this invention includestructure and steps for connecting optical ring networks using a firstring network including a plurality of optical network switches and asecond ring network including a plurality of optical network switches.At least one of the optical network switches is a member of both ringnetworks and passes information between the first and second ringnetworks.

[0014] In another embodiment consistent with the present inventionstructure and steps are provided that connect two optical ring networkswith two switches where a protection line between the two switches isshared by both ring networks.

[0015] In another embodiment consistent with the invention, structureand steps are provided that add and/or remove optical carrier lines froma network, where the network includes a plurality of switches having oneor more optical carrier lines between each pair of switches. A requestfor changing a line between two switches is received from a systemadministrator at one of the switches. The switch determines whether thechange results in a total line bandwidth between the two switches in thenetwork. The switch executes the line change when the change results ina total line bandwidth between the two switches being equal to a totalline bandwidth between other switches in the network.

[0016] Both the foregoing general description and the following detaileddescription explain examples of the invention and do not, by themselves,restrict the scope of the appended claims. The accompanying drawings,which constitute a part of this specification, illustrate systems andmethods consistent with the invention and, together with thedescription, help explain the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The accompanying drawings, which are incorporated in andconstitute part of this specification, illustrate embodiments of theinvention and, together with the description, serve to explain theadvantages of the invention. In the drawings,

[0018]FIG. 1 shows a bi-directional line switched ring according to theprior art;

[0019]FIG. 2 shows two connected bi-directional rings according to theprior art;

[0020]FIG. 3 shows a virtual line switched ring in accordance with thepresent invention;

[0021]FIG. 4 shows a switch and line card in accordance with the presentinvention;

[0022]FIG. 5 shows two connected virtual line switched rings inaccordance with the present invention;

[0023]FIG. 6 shows three connected virtual line switched rings sharing aprotection line in accordance with the present invention;

[0024]FIG. 7 shows a virtual line switched ring having varying numbersand types of lines between switches in accordance with the presentinvention;

[0025]FIG. 8 shows the steps of adding a line to a virtual line switchedring in accordance with the present invention;

[0026]FIG. 9 shows the steps for deleting a line form a virtual lineswitched ring in accordance with the present invention;

[0027]FIG. 10 shows the steps for validating a new line configuration ina virtual line switched ring in accordance with the present invention;

[0028]FIG. 11 illustrates a process for assigning working lines toprotection lines; and

[0029]FIG. 12 illustrates two SONET ring networks configured inaccordance with a feature of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0030] The following detailed description refers to the accompanyingdrawings. The same reference numbers in different drawings identify thesame or similar elements. Also the following detailed description doesnot limit the invention. Instead, the scope of the invention is definedby the appended claims.

[0031] Systems and methods consistent with the principles of the presentinvention provide a SONET ring network that uses switches at the nodesallowing for sharing a switch to connect a plurality of rings. Thepresent invention also provides for sharing a protection line between aplurality of rings by utilizing overhead provided for in the SONETstandard. Finally, the present invention provides for having a differentnumber and type of lines between nodes by using switches and analgorithm to regulate the updating of the lines.

[0032] The present invention, as shown in FIG. 3, uses switches as nodesin a SONET network. For example, SONET ring 300 includes switches 310,320, 330 and 340 coupled to various working and protection lines.Specifically, there are two working lines and two protection linesbetween each pair of switches. Information is transferred through SONETring 300, typically in a time division multiplexed fashion, throughpluralities of input and output ports in each switch.

[0033]FIG. 4 shows an example of a switch consistent with the presentinvention. Switch 410 includes controller 412, manager module 413, spanwest lines 414, span east lines 416, and dispatcher circuit 418.Controller 412 oversees general operations at the switch 410 and is usedby manger module 413 and dispatcher 418 to process and forwardinformation. Manger module 413 manages virtual lines of span west lines514 and span east lines 416. Dispatcher 418 receives and process datafrom external sources.

[0034] Switch 410 is connected to a line card 420 having an aggregator422 and a plurality of monitor modules 424 ₁ to 424 _(n). Aggregator 422gathers information from monitor modules 424 and passes the informationto appropriate switches via monitor modules 424. Each monitor module 424has a plurality of physical SONET lines 430 that connect to otherswitches. Physical lines 430 are logically designated by switch 410 tocorrespond to virtual lines associated with the span west lines 414 andspan east lines 416. Span west lines 414 and span east lines 416 definethe logical mapping between physical lines and logical lines, where thelogical lines may come from any combination of monitor modules 424. Thedesignation of west and east lines is only a logical designation. Thislogical designation is used to distinguish between the different networknodes to which switch 410 is connected. In one embodiment, the span westlines 414 define logical lines leading to one switch in the network,while the span east lines 416 define logical lines leading to anotherswitch in the network.

[0035] Since switch 410 simultaneously transfers information between aplurality of different SONET lines of information, the present inventionallows for two rings to share a switch, or be connected by sharing aswitch. For example, as seen in FIG. 5, SONET network ring 500 and SONETnetwork ring 510 are connected by sharing switch 508. Ring 500 includesswitches 502, 504, 506, and 508. Ring 510 includes switches 508, 512,514, and 516. By using a single switch to connect rings, information ispassed over SONET lines at the same rate between rings as is passedwithin a single ring.

[0036] More than two SONET rings may share a switch. As shown in FIG. 6,three SONET rings share two switches. Ring 600 includes switches 601,602, 603, and 604. Ring 610 includes switches 603, 604, and 612. Ring620 includes switches 603, 604, 622, 624, and 626. As furtherillustrated in FIG. 6, each working and protect line in ring 600 isassigned a particular identifier, e.g., working line one (w1) andprotection line 1 (p1).

[0037] In addition to sharing switches among rings, the rings of FIG. 6share protection line p4 (605). Moreover, between each switch and itsneighbor there is a working line, which is shown as a solid line, and aprotection line, which is shown as a dotted line. Three working linesconnect switch 603 to switch 604, one for each ring, and one protectionline 605 which is shared by all of the rings. The sharing of aprotection line is not required between these switches; three dedicationprotection lines could have been provided between these two switchesinstead. When rings share a protection line, however, the protectionline is allocated for use on a first-come, first served basis.Individual STS-1 segments on the protection line are allocated toreplace the working lines on an STS-1 segment basis. One protection linemay carry portions of STS-1 segments from more than one working line.

[0038] Multiple rings may share a protection line by utilizing K-bytesignaling on multiple STS-1 segments. As previously discussed, K-bytescarry error information related to line failures for a ring. Errorsnoted in the K-byte may initiate switching between a working andprotection line. For example, criteria for switching between a workingand protection lines are generally the same, and may include loss ofsignal, loss of frame, an alarm indication signal, or a single failure.In which case, K-byte codes may include: block out of protection code,forced span switch code, forced ring switch code, signal fail-span code,signal fail-ring code, and signal degrade code, among others.

[0039] Conventional BLSR only allows for one ring to use a protectionline and only uses the first K-bytes from the first STS-1 in a series ofSTS-1 segments to report errors for the single ring. Even though notused, the current SONET protocol includes K-byte overhead in each STS-1of a series of STS-1 segments for additional rings. The presentinvention uses these K-bytes in the succeeding STS-1 segments to realizeshared protection lines. In particular, each ring has separate K-byteinformation to reflect errors within the ring. When one or more ringsuse a protection line, the K-byte information is carried over thatprotection line for each ring, and is carried in respective sequentialSTS-1 segments. The switches on either end of the protection line thatis being shared are programmed with information defining which STS-1segment is carrying the K-byte information for which ring. For example,the first segment may contain the K-byte information for ring 610, andthe third segment contains the K-byte information for ring 620. Switches603 and 604 are thus programmed with information defining which STS-1segment carries the K-byte information for which ring based on thereceived order of the STS-1 segments. In addition, K-byte informationconcerning the availability of a particular protection line is passed toother switches in the rings through appropriate signalling, as discussedin greater detail below.

[0040] Returning to FIG. 4, monitor module 424 monitors incomingK-bytes. More particularly, monitor module 424 monitors incoming K-bytesfor changes indicating an error. When a K-byte change for a particularring is maintained for at least three consecutive frames monitor module424, monitor module 424 reads the value of the K-bytes and sends thechange to aggregator 422. Aggregator 422 queues the K-byte informationfrom other monitor modules 424, and after a period of time, such as onemillisecond, sends a message to switch 410 that includes the K-bytechanges, and the lines that have signal failure or degradation.Dispatcher 418 parses the message from the aggregator 422 and sends lineinformation to span west lines 414 or span east lines 416 if either ofthese utilize the line in question. The span receiving the lineinformation may do nothing if higher priority conditions exist, or mayinitiate a line switch, ring switch, or route change.

[0041]FIG. 11 illustrates steps of a process 11 for mapping workinglines to corresponding protections lines. The mapping is performed on afirst-come, first served basis, and should conform to an orderingdictated by a network administrator. In a first step 1110, a first STS-1on a first working line is mapped to a first STS-1 of a first protectionline. In step 1120, the next STS-1 of the working line is mapped to thenext available STS-1 of a protection line. Each remaining STS-1 of theworking line is mapped to a respective STS-1 on a protection line (step1130). Steps 1110 through 11130 are repeated for each remaining workingline (step 1140).

[0042] The invention will next be described by way of example withreference to FIG. 12 showing first and second rings 1200 and 1205.Within ring 1200, working traffic originating at switch 1230 andterminating at switch 1220 is passed along span 1225 in a east-westdirection as indicated by arrow 1226. If a break occurs in span 1226 (asindicated by an “X”), traffic is rerouted through switches 1210 and 1240using a shared protection line in span 1227, which is assigned inaccordance with processes and structures identified above. In this case,a K-byte ring switch signal is supplied from switch 1230 to switch 1240and then to switches 1210 and 120 to thereby indicate use of theprotection line in ring 1205, at least for particular time slots soaffected by the break in span 1226. Switch elements in ring 1200,however, must further follow an arbitration protocol whereby theprotection line in span 1227 is rendered not available to them, at leastfor those time slots. Accordingly, switch 1230 passes known K-bytelockout-protection span (LP-S) data to switch 1240, which in turn,forwards this data to remaining switches 1260 and 1250 in ring 1200.Thus, information concerning availability of a particular protectionline, as well, as information concerning a fault in a particular span isdistributed amongst the switching elements of a given network throughK-byte signaling.

[0043] In another embodiment, systems and methods consistent with theprinciples of the present invention utilize a varying number and type oflines between switches in a SONET ring network. As discussed above,current SONET networks require the same number of optical carrier leveltype of lines between nodes. The present invention, however, allows fordifferent combinations of optical carrier lines between switches,thereby providing greater network flexibility. Switch 410 has aplurality of ports and can split information from one line into manylines, or combine information from many lines and output the informationon a single line. As shown in FIG. 7, SONET ring network 700 hasswitches 710, 720, 730, and 740. The connections between these switchesare not the same for every span. For example, between switch 710 andswitch 720, there are two optical carrier 12 (OC-12) working lines ineach direction. Between switch 720 and switch 730, there is one OC-48working line going in each direction between the switches. Consistentwith the present invention, any combination of optical carrier levelsmay be combined between spans as long as the total capacity of the spanbetween two switches equals the total capacity between other switches inthe ring. In addition, the sum of the capacities of the working linesbetween two switches must equal the sum of the capacities of theprotection lines between the switches. In the ring network shown in FIG.7, for example, the sum of the optical capacities between each set ofswitches is a total of OC-48. This total may be reached using anycombination of OC carrier lines. For example, the spans between switches710 and 720 reach this total using four OC-12 lines while the spansbetween switches 720 and 730 reach this total using one OC-48 line.Switches 710, 720, 730, 740 direct traffic from a single OC-48 to fourOC-12 lines.

[0044] Moreover, in accordance with the present invention, lines mayeasily be added or removed from the ring. However, before a line is madeactive or inactive, the switches on both sides of the line determinewhether the line change maintains the required optical carrier capacitybetween switches. FIG. 8 shows the steps 800 performed by manager module413 when adding a line. First, a system administrator specifies the lineto made active by inputting a request, including a line identifier, intomanager module 413 at a switch at either end of the new line (step 810).This line ID must be the same on both ends of the line. All of theswitches identify the line using the same identifier, as discussed abovewith respect to FIG. 6. Manger module 413 determines the state of thespecified line from the monitor modules 424 (step 820). Monitor modules424 maintain information regarding the state of each line based on theline identifier. Lines are only used for actual transmission when in theactive state. The activating state refers to the state before monitormodules 424 on either side of a line have agreed to placing a line inthe active state. Similarly, the deactivating state is the state beforethe monitor module have agreed to placing a line in the inactive state.When a line is physically added, the monitor module 424 automaticallydesignates the line as being in an inactive state. If the line to beadded is in fact inactive, then the line is moved to the activated state(step 830). If however, the specified line is already in the activatingstate, then manager module 413 ignores the request (step 840). If theline specified is already active, then manager module 413 logs an errorin a central accessible log (step 850). If the specified line is in adeactivating state, then manager module 413 directs the monitor module424 to place the line back in the active state (step 860).

[0045]FIG. 9 shows the steps 900 performed by manager module 413 whendeleting a line. First, a system administrator specifies the line to bedeleted by inputting a request, including a line identifier, intomanager module 413 at a switch at either end of the line (step 910).Manager module 413 queries monitor module 424 to determine the status ofthe specified line (step 920). If the specified line is inactive, thenmanager module 413 takes an error in a central accessible log and doesnot take further action (step 930). If the designated line is in theactivating state, then manager module 413 directs monitor module 424 torevert the line to an inactive state (step 940). If the specified lineis in the active state, then manager module 413 directs monitor module424 to place the BLSR line in a deactivating state (step 950). If thespecified line is already in the deactivating state, then manager module413 ignores the request (step 960).

[0046]FIG. 10 shows steps 1000 performed by manager module 413 whenvalidating a new configuration of lines after lines have been added ordeleted. To validate the configuration, manager module 413 first sumsthe capacity of the lines associated with span west lines 416 that arein the active state or activating state (step 1020). The sum of thecapacity of the active lines in the span west lines 414 should equal thesummation of the capacity of the active lines in the span east lines416. Manager module 413 determines whether these sums are equal (step1030) and, if not, an error is generated and logged (step 1040). If thesums are equal, then manager module 413 directs monitor modules 424 tomove all of the lines in the activating state to the active state (step1050). Similarly, manager module 413 directs the monitor modules to moveall the lines in the deactivating state to the inactive state (1060).Manager module 413 in each switch in the ring network performs thischeck before validating any configuration.

[0047] In conclusion, the SONET ring network of the present inventionuses switches as the network nodes to allow sharing a switch to connecta plurality of rings. A protection line between a plurality of rings isshared by utilizing overhead provided for in SONET standard protocols.Moreover, the shared protection line can be used by one ring over afirst time slot and a second ring over a second time slot. Thus,capacity which would otherwise be used for carrying dedicated protectiontraffic is utilized by additional working traffic instead. As a result,network capacity is increased without adding more physical lines.Finally, the present invention provides for having a different numberand type of lines between switches in a ring network by using switchesand an algorithm to regulate the updating of the lines.

[0048] Other embodiments will be apparent to those skilled in the artfrom consideration of the specification and practice of the inventiondisclosed herein. It is intended that the specification and examples beconsidered as exemplary only, with a true scope and spirit of theinvention being indicated by the following claims.

What is claimed is:
 1. A communication system comprising: a first switchconfigured to be coupled to a first network and a second network; and asecond switch configured to be coupled to said first network and saidsecond network and spaced from said first switch, said first and secondnetworks having working lines and protection lines, at least one of saidprotection lines being coupled between said first and second switchesand shared by said first and second networks.
 2. A communication systemin accordance with claim 1, wherein said first and second networks carrydata in accordance with a SONET standard.
 3. A communication system inaccordance with claim 2, wherein said first and second switches furthercomprise: first circuitry in said first switch, said first circuitrybeing configured to transmit fault-related information in a plurality offrames to said second switch; and second circuitry in said secondswitch, said second circuitry being configured to sense saidfault-related information, said first and second switches being furtherconfigured to allocate said shared protection line to one said first andsecond networks in accordance with said fault-related information.
 4. Acommunication system in accordance with claim 3, wherein said pluralityof frames correspond to K-byte portions of a SONET overhead associatedwith a plurality of successive STS-1 time slots.
 5. A communicationsystem in accordance with 3, wherein said first and second circuits areconfigured to conduct an arbitration protocol according to SF-P.
 6. Acommunication system in accordance 3, wherein said first and secondnetworks comprise third and fourth switches, respectively, at least oneof said first and second switches passing said fault-related informationto third and fourth switches.
 7. A communication system in accordancewith claim 1, wherein said first and second switches includes: a linecard having a monitor module associated with a corresponding pluralityof physical optical lines, wherein each of said first and secondswitches maintains a logical association to a subset of the physical andoptical lines.
 8. A communication system in accordance with claim 1,wherein said first and second networks have a ring configuration.
 9. Acommunication method comprising the steps of: monitoring failure relatedinformation associated with a working segment of a first communicationnetwork; and assigning a protection segment of said first communicationnetwork to carry data associated with said working segment of said firstcommunication network, said protection segment being common to a secondcommunication network.
 10. A communication method in accordance withclaim 9, further comprising a step of transmitting said data throughsaid working segment in accordance with a SONET standard.
 11. Acommunication method in accordance with claim 10, wherein saidmonitoring step comprises the step of detecting K-byte data in aplurality of succeeding STS-1 time slots.
 12. A communication method inaccordance with claim 10, further comprising the step of conducting anarbitration in accordance with SF-P concerning said shared protectionline.
 13. A communication method in accordance with claim 10, whereinsaid assigning step comprises the steps of: assigning said protectionline to said first network over a first time slot; and assigning saidprotection line to said second network over a second time slot.
 14. Acommunication method in accordance with claim 9, further comprising thestep of distributing data concerning said shared protection line amongpluralities of switch elements in said first and second networks.
 15. Acommunication method in accordance with claim 9, wherein said first andsecond networks have a ring configuration.